The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
In many modern automotive transmissions, especially dual clutch transmissions (DCT's), a plurality of hydraulic actuators (operators) carry out commands that provide both a desired shift and shift sequence. In order to control such operators and confirm the attainment of a desired position, it is common practice to employ plural state or proportional linear position sensors that, in the former case, provide, for example, a signal that changes from a first state to a second state when a particular operator position has been achieved and, in the latter case, provide a signal that varies linearly (proportionally) between a first actuator position and a second actuator position. The proportional sensors generate data that indicates when multiple distinct actuator positions have been achieved and provide the real time position of the actuator during translation and, if differentiated, the speed of the actuator.
In a typical magnetic field linear sensor assembly, a permanent magnet is mounted to a translating component such as the actuator piston, the output shaft or an associated shift rail and the magnetic sensor, which is stationary, is secured in proximate, sensing relationship with the permanent magnet to a housing, flange, web or other stationary transmission component. Translation of the permanent magnet thus varies the magnetic field strength sensed by the sensor and, with proper conditioning, scaling and software, the position of the actuator and associated shift components can be determined.
A concentric slave cylinder assembly having concentric piston rings is often used to actuate two clutches that are located near each other, such as in a DCT that have two input shafts, wherein each input shaft provides a subset of the available gear ratios. Each input shaft is selectively coupled to an engine by the use of one of these clutches. The pistons are designed to travel linearly. The linear travel of each piston is sensed by a sensor assembly, as described above, to measure the stroke of each piston. However, any non-linear movement is also sensed by such sensors and may be result in an inaccurate measurement of the piston position. When the piston position is inaccurately measured, clutch apply pressure is erroneously adjusted, which may result in shift flares or firm shift applies. Accordingly, more accurate measurement of piston stroke is desired.